1. Field of the Invention
This invention relates to a novel group of chemical compounds which are steroid derivatives of isostearyl carbonate, to the use thereof as solidification retarders in liquid crystalline compositions, to the solidification retarded compositions, to the manufactured articles made therefrom.
2. Description of the Prior Art
Liquid crystals may be defined as that class of matter which has an intermediate or mesomorphic state in which these substances behave mechanically as liquids yet exhibit many optical properties of crystals. The mesomorphic state or liquid crystalline phase is obtained either by heating liquid crystals that are in the solid phase or by cooling liquid crystals that are in the liquid phase. Liquid crystal substances have been classified as belonging in one of three different types, viz., cholesteric, nematic and smectic. The cholesteric structure is distinguished from the nematic and smectic structures by its markedly different optical properties, for example, cholesteric materials are optically negative whereas nematic and smectic materials are optically positive.
Thin films of cholesteric liquid crystals upon interaction with light exhibit a property, termed selective scattering, whereby light rays impinging upon the film may leave at an angle unrelated to the angle of incident light. The color and intensity of the scattered light depends upon the temperature of the scattering material and upon the angle of incident illumination. The range of temperatures within which visible colors are displayed as a result of scattering of white light from cholesteric liquid crystals is known as the color play range. A color play range may be made as wide as 30.degree. C. or more (for example, start of red at 37.degree. C. through the visible color spectrum with start of blue at 67.degree. C.) or may be as narrow as 1.degree. C. (for example, start of red at 30.degree. C. through the visible color spectrum with start of blue at 31.degree. C.).
Many liquid crystalline materials having once been melted, tend to solidify in a short period of time. U.S. Pat. No. 3,580,864 describes the use of a compound, cholesteryl erucyl carbonate, to stabilize cholesteric-phase liquid-crystal compositions against true-solid formation. However, perhaps because of the erucyl carbon-carbon double bond, this compound is not as able to resist ultraviolet light degradation as are the novel compounds of this invention.
The production of steroid alkyl carbonates is well known to persons skilled in the art of steroid synthesis. By way of example one method, but not necessarily the preferred, involves the reaction of alkyl chloroformate (either as a reagent or synthesized in situ by the reaction of phosgene with an alkanol) with pyridine and a sterol. Insoluble pyridine hydrochloride which is precipitated is filtered from the reaction mixture. The oily alkyl steroid carbonate layer is separated from the filtrate by means of a separatory funnel and repeatedly washed with methanol.